<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    .parent{
        width: 0px;
        height: 0px;
        border: 20px solid transparent;
        border-top-color: black;
        position: relative;    
    }
    .parent::before{
        content: "";
        width: 0px;
        height: 0px;
        display: block;
        border: 20px solid transparent;
        border-top-color:white;
        position: absolute;
        left: 50%;
        margin-left: -20px;
        top: -22px;
    }
    </style>
</head>
<body>
    <div class="parent">

    </div>
</body>
</html>